The present invention relates to an improved process for the copolymerization of alkylene oxides and carbon dioxide using multimetal cyanide compounds as catalysts. The present invention permits one to efficiently form polyethercarbonate polyols with better incorporation of carbon dioxide into the polyol.
Polyethercarbonate polyols are the polymerization reaction product of an initiator, at least one alkylene oxide and carbon dioxide. The carbon dioxide is incorporated into the backbone of the polyol chain. A number of catalyst systems have been used to form polyethercarbonate polyols with varying degrees of success. One difficulty has been the generally low reactivity of carbon dioxide in the catalytic systems to date, in particular the generally observed decreasing rate of reaction with increasing CO2 pressure (L Chen, Rate of regulated copolymerization involving CO2, J Natural Gas Chemistry, 1998, 7, 149-156), thus requiring very high levels of catalyst to produce any product having incorporation of a significant amount of carbon dioxide into the polyol. A second difficulty is the generally high rate of formation of cyclic by products such as propylene carbonate. Finally, most procedures produce a very viscous product having a large degree of polydispersity.
In an attempt to better control the reaction and to increase the carbon dioxide incorporation, several forms of double metal cyanide (DMC) complexes have been used in the past. These are disclosed in the following U.S. Pat. Nos. 4,472,560; 4,500,704; 4,826,887; 4,826,952; and 4,826,953. These DMC procedures, however, still suffer from slow reaction rates, required high catalyst concentrations and have high levels of by-product formation. Polyethercarbonate polyols produced using these DMC catalysts also have high viscosities and high degrees of polydispersity. Thus there is a need for an improved catalyst system for polyethercarbonate polyol formation.
Most double metal cyanide complexes are amorphous structures and are used in the form of powders. In the present invention it has been found that much better results are obtained using crystalline multimetal cyanide compounds in a form which gives them a very high catalytic activity. In a preferred embodiment crystalline multimetal cyanide compounds are suspended in organic or inorganic liquids and used as catalysts in this form. It is particularly advantageous for the suspended multimetal cyanide compound to have a platelet-like morphology.
In one embodiment, the present invention is a method of forming a polyethercarbonate polyol comprising the steps of: providing a multimetal cyanide compound having a crystalline structure and a content of platelet-shaped particles of preferably at least 30% by weight, based on the weight of the multimetal cyanide compound and further comprising at least two of the following: an organic complexing agent, water, a polyether, and a surface-active substance; and reacting an alcohol initiator with at least one alkylene oxide and carbon dioxide under a positive pressure in the presence of the multimetal cyanide compound, thereby forming the polyethercarbonate polyol.
In the present invention a unique multimetal cyanide compound is used. The compound is crystalline and preferably has a platelet-like morphology. In addition, the catalyst is preferably used in the form of a suspension, which gives it unique activity. The multimetal cyanide compound of the present invention provides different activity than past DMC complexes.
The multimetal compound of the present invention comprises at least three components. First, at least one multimetal cyanide compound having a crystalline structure and a content of platelet-shaped particles of at least 30% by weight, based on the multimetal cyanide compound. Second the compound includes at least two of the following components: an organic complexing agent, water, a polyether, and a surface-active substance.
The organic complexing agent comprises, in particular, one of the following: alcohols, ethers, esters, ketones, aldehydes, carboxylic acids, amides, nitrites, sulfides and mixtures thereof.
As polyethers, use is made, in particular, of polyether alcohols, preferably hydroxyl-containing polyaddition products of ethylene oxide, propylene oxide, butylene oxide, vinyloxirane, tetrahydrofuran, 1,1,2-trimethylethylene oxide, 1,1,2,2-tetramethylethylene oxide, 2,2-dimethyloxetane, diisobutylene oxide, xcex1-methylstyrene oxide and mixtures thereof.
As the surface-active substance, use is made, in particular, of compounds selected from the group comprising C4-C60-alcohol alkoxylates, block copolymers of alkylene oxides of differing hydrophilicity, alkoxylates of fatty acids and fatty acid glycerides, block copolymers of alkylene oxides and polymerizable acids and esters.
The crystalline multimetal cyanide compounds used according to the present invention are preferably prepared by the following method. First, addition of an aqueous solution of a water-soluble metal salt of the formula M1m(X)n to an aqueous solution of cyanometalate compound of the formula HaM2(CN)b(A)c. Wherein for the formula M1m(X)n: M1 is at least one metal ion selected from the group consisting of Zn2+, Fe2+, Co3+, Ni2+, Mn2+, Co2+, Sn2+, Pb2+, Fe3+, Mo4+, Mo6+, Al3+, V5+, Sr2+, W4+, W6+, Cu2+, Cr2+, Cr3+, Cd2+, Hg2+, Pd2+, Pt2+, Vt2+, Mg2+, Ca2+, Ba2+, and mixtures thereof; X is at least one anion selected from the group consisting of halide, hydroxide, sulfate, carbonate, cyanide, thiocyanate, isocyanate, carboxylate, in particular formate, acetate, propionate or oxalate; and nitrate and m and n are integers which satisfy the valence of M1, and X. Wherein for the formula HaM2(CN)b(A)c,: M2 is at least one metal ion selected from the group consisting of Fe2+, Fe3+, Co3+, Cr3+, Mn2+, Mn3+, Rh3+, Ru2+, Ru3+, V4+, V5+, Co2+, Ir3+, and Cr2+ and M2 can be identical to or different from M1; H is hydrogen or a metal ion, usually an alkali metal ion, an alkaline earth metal ion or an ammonium ion; A is at least one anion selected from the group consisting of halide, hydroxide, sulfate, carbonate, cyanate, thiocyanide, isocyanate, carboxylate and nitrate, in particular cyanide, where A can be identical to or different from X; and a, b and c are integers selected so that the cyanide compound is electrically neutral.
In an alternative, one or both aqueous solutions may, if desired, comprise at least one water-miscible, heteroatom-containing ligand selected from the group comprising alcohols, ethers, esters, ketones, aldehydes, carboxylic acids, amides, sulfides or mixtures of at least two of the components mentioned, and at least one of the two solutions comprises a surface-active substance.
Also if desired, combination of the aqueous suspension formed in the first step above can be made with a water-miscible, heteroatom-containing ligand selected from the above-described group which can be identical to or different from the ligand in the first step.
In a second step, if desired, the multimetal cyanide compound can be separated from the suspension.
The procedure produces platelet-like shaped crystalline multimetal cyanide compounds. The compounds can have a cubic, tetragonal, trigonal, orthorhombic, hexagonal, monoclinic or triclinic crystal structure. The definition of the crystal systems describing these structures and the space groups belonging to the abovementioned crystal systems may be found in xe2x80x9cInternational tables for crystallographyxe2x80x9d, Volume A, editor: Theor Hahn, (1995).
For the preparation of multimetal cyanide compounds which are used for the suspensions of the present invention, it is advantageous, but not necessary, to use the cyanometalic acid as a cyanometalate compound, since this does not result in formation of a salt as a by-product.
These cyanometalic acids (hydrogen cyanometalates), which are preferably used, are stable and readily handeable in aqueous solution. They can be prepared, for example as described in W. Klemm, W. Brandt, R. Hoppe, Z. Anorg, Allg. Chem. 308, 179 (1961), starting from the alkali metal cyanometalate via the silver cyanometalate and then to the cyanometalic acid. A further possibility is to convert an alkali metal or alkaline earth metal cyanometalate into a cyanometalic acid by means of an acid ion exchanger, as described, for example, in F. Hein, H. Lilie, Z. Anorg, Allg. Chem. 270, 45 (1952), or A. Ludi, H. U. Gxc3xcdel, V. Dvorak, Helv. Chim, Acta 50, 2035 (1967). Further possible ways of synthesizing the cyanometalic acids may be found, for example, in xe2x80x9cHandbuch der Prxc3xa4parativen Anorganischen Chemiexe2x80x9d, G. Bauer (editor), Ferdinand Enke Verlag, Stuttgart, 1981. For an industrial preparation of these compounds, as is necessary for the process of the present invention, the synthesis via ion exchangers is the most advantageous route. After they have been synthesized, the cyanometalic acid solutions can be processed further immediately, but it is also possible to store them for a relatively long period. Such storage should be carried out in the absence of light to prevent decomposition of the acid.
The proportion of the acid in the solution should be greater than 80% by weight, based on the total mass of cyanometalate complexes, preferably greater than 90% by weight, in particular greater than 95% by weight.
As heteroatom-containing ligands, use is made of the above-described organic substances. In a preferred embodiment of the preparation process, no heteroatom-containing ligand is added to the solutions in the first step and the addition of heteroatom-containing ligand to the suspension of precipitate is also omitted in the second step. In a preferred embodiment, only the at least one surface-active component is added, as mentioned above, to one or both of the solutions in the first step.
The surface-active compounds used according to the present invention can be anionic, cationic, nonionic and/or polymeric surfactants. In particular, nonionic and/or polymeric surfactants are used. Compounds selected from this group are, in particular, fatty alcohol alkoxylates, block copolymers of various epoxides having differing hydrophilicity, castor oil alkoxylates or block copolymers of epoxides and other monomers, e.g. acrylic acid or methacrylic acid.
Fatty alcohol alkoxylates used according to the present invention have a fatty alcohol comprising 8-36 carbon atoms, in particular 10-18 carbon atoms. This is alkoxylated with ethylene oxide, propylene oxide and/or butylene oxide. The polyether part of the fatty alcohol alkoxylate used according to the present invention can consist of pure ethylene oxide, propylene oxide or butylene oxide polyethers. Furthermore, it is also possible to use copolymers of two or three different alkylene oxides or else block copolymers of two or three different alkylene oxides. Fatty alcohol alkoxylates which have pure polyether chains are, for example, Lutensol AO grades from BASF AG. Fatty alcohol alkoxylates having block copolymers as polyether part are Plurafac LF grades from BASF Aktiengesellschaft. The polyether chains particularly preferably consist of from 2 to 50, in particular from 3 to 15, alkylene oxide units.
Block copolymers as surfactants comprise two different polyether blocks which differ in their hydrophilicity. Block copolymers which can be used according to the present invention may comprise ethylene oxide and propylene oxide (Pluronic grades, BASF Aktiengesellschaft). The water solubility is controlled via the lengths of the various blocks. The molar masses are in the range from 500 Da to 20,000 Da, preferably from 1,000 Da to 6,000 Da and in particular 1,500-4,000 Da. In the case of ethylene-propylene copolymers, the proportion of ethylene oxide is from 5 to 50% by weight and the proportion of propylene oxide is from 50 to 95% by weight.
Copolymers of alkylene oxide with other monomers which can be used according to the present invention preferably have ethylene blocks. The other monomer can be, for example, butyl methacrylate (PBMA/PEO BE1010/BE1030, Th. Goldschmidt), methyl methacrylate (PMMA/PEO ME1010/ME1030, Th. Goldschmidt) or methacrylic acid (EA-300, Th. Goldschmidt).
The surface-active substances used should have a moderate to good solubility in water.
To prepare the crystalline multimetal cyanide compounds used according to the present invention, an aqueous solution of a cyanometalic acid or of a cyanometalate salt is combined with the aqueous solution of a metal salt of the formula M1m(X)n, where the symbols are as defined above. Here, a stoichiometric excess of the metal salt is employed. The molar ratio of the metal ion to the cyanometalate component is preferably from 1.1 to 7.0, more preferably from 1.2 to 5.0 and particularly preferably from 1.3 to 3.0. It is advantageous to place the metal salt solution in the precipitation vessel first and to add the cyanometalate compound, but the reverse procedure can also be used. During and after combining the starting solutions, good mixing, for example by stirring, is necessary.
The content of the cyanometalate compound in the cyanometalate starting solution based on the mass of cyanometalate starting solution is from 0.1 to 30% by weight, preferably from 0.1 to 20% by weight, in particular from 0.2 to 10% by weight. The content of the metal salt component in the metal salt solution based on the mass of metal salt solution is from 0.1 to 50% by weight, preferably from 0.2 to 40% by weight, in particular from 0.5 to 30% by weight.
The surface-active substances are generally added beforehand to at least one of the two solutions. The surface-active substances are preferably added to the solution which is initially charged in the precipitation. The content of surface-active substances in the precipitation solution based on the total mass of the precipitation suspension is from 0.01 to 40% by weight. Preference is given to a content of from 0.05 to 30% by weight.
A further preferred embodiment provides for the surface-active substances to be divided proportionately among the two starting solutions.
The heteroatom-containing ligands are, in particular, added to the suspension formed after combination of the two starting solutions. Here too, good mixing has to be ensured.
It is also possible, however, to add all or some of the ligand to one or both starting solutions. In this case, owing to the change in the salt solubility, the ligand is preferably added to the solution of the cyanometalate compound.
The content of the ligand in the suspension formed after the precipitation should be from 1 to 60% by weight, preferably from 5 to 40% by weight, in particular from 10 to 30% by weight.
The multimetal cyanide compounds used according to the present invention preferably have X-ray diffraction patterns as are shown in FIGS. 3 and 4 of DE 197 42 978.
The multimetal cyanide compounds used for preparing the suspensions of the present invention preferably comprise primary crystals having a platelet-like morphology. For the purposes of the present invention, platelet-shaped particles are particles whose thickness is one third, preferably one fifth, particularly preferably one tenth, of their length and width. The preferred catalyst according to the present invention contains more than 30% by weight of such platelet-shaped crystals, preferably more than 50% by weight, particularly preferably more than 70% by weight and very particularly preferably more than 90% by weight. The preferred multimetal cyanide compounds according to the present invention can be seen in scanning electron micrographs.
Multimetal cyanide compounds which are less preferred according to the present invention are often either in rod form or in the form of small cube-shaped or spherical crystals.
Depending on how pronounced the platelet character of the particles is and how many are present in the catalyst, it is possible that distinct to strong intensity changes in the individual reflections in the X-ray diffraction pattern compared to rod-shaped multimetal cyanide compounds of the same structure will occur.
The multimetal cyanide compounds produced by precipitation according to the above-described process can then be separated from the suspension by filtration or centrifugation. After the separation, the multimetal cyanide compounds can then be washed one or more times. Washing can be carried out using water, the abovementioned heteroatom-containing ligands or mixtures thereof. Washing can be carried out in the separation apparatus (e.g. filtration apparatus) itself or be carried out in separate apparatuses, by, for example, resuspension of the multimetal cyanide compound in the washing liquid and separating it from the liquid again. This washing can be carried out at from 10xc2x0 C. to 150xc2x0 C., preferably from 15 to 60xc2x0 C.
The multimetal cyanide compound can subsequently be dried at from 30xc2x0 C. to 180xc2x0 C. and pressures of from 0.001 bar to 2 bar, preferably from 30xc2x0 C. to 100xc2x0 C. and pressures of from 0.002 bar to 1 bar. Drying can also be omitted, in which case a moist filter cake is obtained.
A preferred embodiment of the preparation process for the multimetal cyanide compound used according to the present invention provides for no organic, heteroatom-containing ligand, as has been defined above, apart from the surface-active substance to be added before, during or after the precipitation. In this embodiment of the preparation process, in which no further organic, heteroatom-containing ligands apart from the surface-active substance are used, the multimetal cyanide compound is washed with water after separation from the precipitation suspension.
The multimetal cyanide compounds prepared as described above are used in the form of the suspensions of the present invention for preparing polyethercarbonate polyols.
Both the moist and the dried multimetal cyanide compounds can be used as starting materials for the suspensions of the present invention. The pulverulent, dried multimetal cyanide compounds are, to prepare the suspensions of the present invention, dispersed as finely as possible in the suspension liquid by an efficient dispersion procedure in order to achieve a very high activity of the multimetal cyanide catalyst. Such methods of efficiently producing a very finely dispersed suspension are, inter alia, stirring under high shear forces, e.g. in homogenizers or Ultraturrax apparatuses, and also the use of dispersion machines, in particular ball mills and agitated ball mills, e.g. bead mills in general and particularly those having small milling beads (e.g. 0.3 mm diameter) such as the double-cylinder bead mills (DCP-Super Flow(copyright)) from Draiswerken GmbH, Mannheim, or the centrifugal fluidized bed mills from Netzsch Gerxc3xa4tebau GmbH, Selb. If desired, dissolvers can be used for predispersion. Furthermore, small amounts of dispersants known to those skilled in the art, e.g. lecithin, zinc oleate or zinc stearate, can be used. In addition, all methods which allow the powder to be dispersed very finely in liquids are suitable. Dispersion can be carried out at from 10xc2x0 C. to 150xc2x0 C., preferably from 30xc2x0 C. to 120xc2x0 C. Dispersion liquids which can be used are polyethers, organic liquids or water, and also mixtures thereof.
As polyethers for the dispersion, it is possible to use compounds having molar masses of from 150 to 6,000 dalton and functionalities of from 1 to 8. Preference is given to using polyethers having molar masses of from 150 to 2,000 dalton and functionalities of from 1 to 3, in particular molar masses of from 150 to 800 dalton.
If the predried multimetal cyanide compound is suspended in an organic liquid, suspensions having solids contents of less than 10% by weight are preferred. Particular preference is given to solids contents of less than 5% by weight. Organic liquids which can be used are heteroatom-containing compounds and also hydrocarbons or mixtures thereof. Compounds which have a vapor pressure of greater than 0.005 bar at 100xc2x0 C.
If the predried multimetal cyanide compound is suspended in water, preference is given to suspensions having solids contents of less than 20% by weight and pastes having solids contents of less than 60% by weight. The water content of the pastes and suspensions should then be above 20% by weight.
Preference is given to omitting the drying step. In this case, the moist multimetal cyanide compounds are used for preparing the suspensions of the present invention. For this purpose, a suspension is prepared from the moist multimetal cyanide compound after precipitation and separation of the precipitate from the suspension and after washing of the multimetal cyanide compound, either on the filtration apparatus or externally with filtration being repeated again, but without carrying out a drying step. The multimetal cyanide compound can, as in the case of the dried multimetal cyanide compounds, be suspended in the abovementioned dispersion media. The methods of preparing a very finely divided suspension which have been described for the dried multimetal cyanide compounds can also be used for dispersing the undried multimetal cyanide compounds.
When using moist multimetal cyanide compounds for preparing suspensions in at least one polyether or a similarly high-boiling liquid, heat and vacuum can, in a preferred embodiment, be applied simultaneously during the dispersion step in order to remove volatile constituents such as water or organic ligands. In the present context, application of vacuum means both the normal vacuum stripping at pressures down to 0.001 bar and also the combination of vacuum treatment and stripping with inert gases such as nitrogen, argon, helium, etc. The temperature in this step can be from 10xc2x0 C. to 150xc2x0 C., preferably from 30xc2x0 C. to 120xc2x0 C.
In the case of multimetal cyanide suspensions in polyethers, suspensions having solids contents of less than 20% by weight are preferred. Particular preference is given to solids contents of less than 10% by weight, in particular less than 5% by weight. If the undried multimetal cyanide compound is suspended in organic liquids, as described above, suspensions having solids contents of less than 10% by weight are preferred. Particular preference is given to solids contents of less than 5% by weight. If the undried multimetal cyanide compound is suspended in water, suspensions having solids contents of less than 20% by weight and pastes having solids of less than 60% by weight are preferred. The water content of the pastes and suspensions should then be above 20% by weight.
If the starting materials used for preparing the multimetal cyanide compound are cyanometalic acid and, as the metal salt, a salt of an acid which has a vapor pressure of greater than 0.005 bar at 100xc2x0 C., the suspensions of the present invention can be prepared according to the following advantageous embodiment. Here, the precipitation is carried out in the presence of the surface-active agent and optionally the organic ligand. If an organic ligand is used, the organic ligand should likewise have a vapor pressure of greater than 0.005 bar at 100xc2x0 C. After combining the starting material solutions, polyether is added to the precipitation suspension and the acid formed during the precipitation, the water and at least part of the organic ligands are distilled off, if desired under reduced pressure. The remaining suspension has, according to the present invention, a solids content of less than 20% by weight and a polyether content of greater than 80% by weight. The possible polyethers are defined above. Preference is given to polyether alcohols having molar masses of from 150 to 2,000 dalton, so that the resulting suspension can be used directly as catalyst for preparing polyether alcohols.
The multimetal cyanide suspensions prepared by the method according to the present invention are very useful as catalysts for the synthesis of polyethercarbonate polyols having functionalities of from 1 to 8, preferably from 1 to 4, and number average molar weights of from 200 to 20,000. The polyethercarbonate polyols are formed by addition polymerization of alkylene oxides and carbon dioxide onto H-functional initiator substances, like mono-alcohols and poly-alcohols.
To prepare polyethercarbonate polyols using the catalysts of the present invention, it is possible to employ a large number of compounds having at least one alkylene oxide group, for example ethylene oxide, 1,2-epoxypropane, 1,2-methyl-2-methylpropane, 1,2-epoxybutane, 2,3-epoxybutane, 1,2-methyl-3-methylbutane, 1,2-epoxypentane, 1,2-methyl-3-methylpentane, 1,2-epoxyhexane, 1,2-epoxyheptane, 1,2-epoxyoctane, 1,2-epoxynonane, 1,2-epoxydecane, 1,2-epoxyundecane, 1,2-epoxydodecane, styrene oxide, 1,2-epoxycyclopentane, 1,2-epoxycyclohexane, (2,3-epoxypropyl)-benzene, vinyloxirane, 3-phenoxy-1,2-epoxypropane, 2,3-epoxy (methyl ether), 2,3-epoxy (ethyl ether), 2,3-epoxy (isopropyl ether), 2,3-epoxy-1-propanol, 3,4-epoxybutyl stearate, 4,5-epoxypentyl acetate, 2,3-epoxy propyl methacrylate, 2,3-epoxypropyl acrylate, glycidol butyrate, methyl glycidate, ethyl 2,3-epoxybutanoate, 4-(trimethylsilyl)butane 1,2-epoxide, 4-(trimethylsilyl)butane 1,2-epoxide, 3-(perfluoromethyl)propene oxide, 3-perfluoromethyl)propene oxide, 3-(perfluorobutyl)propene oxide, and also any mixtures of at least two of the abovementioned compounds.
The desired carbon dioxide content of the polyethercarbonate polyol is preferably from 1 to 30%, more preferably from 2 to 20%, and most preferably from 5 to 15%, based on weight % of CO3 of the polyethercarbonate polyol. The catalyst concentrations employed are less than 1% by weight, preferably less than 0.5% by weight, particularly preferably less than 1,000 ppm, very particularly preferably less than 500 ppm and especially preferably less than 100 ppm, based on the total mass of the polyethercarbonate polyol. The polyethercarbonate polyols can be prepared either batchwise, semi-continuously or fully continuously. The process temperatures which can be employed in the synthesis are in the range from 40xc2x0 C. to 180xc2x0 C., with preference being given to temperatures in the range from 90xc2x0 C. to 130xc2x0 C. Temperatures above 180xc2x0 C. may result in catalyst decomposition and thus reduce catalyst activity. The carbon dioxide pressure during the reaction influences the amount of carbon dioxide incorporation. The carbon dioxide pressure may vary widely and range from 10 to 3,000 pounds per square inch (psi), preferably from 90 to 2,500 psi, and more preferably from 90 to 2,000 psi.
To prepare the polyethercarbonate polyols using the catalysts of the present invention, it is possible to employ other typical polyol initiator compounds preferably those having at least one alkylene oxide group. Suitable initiator compounds include alkanols such as butanol, diols, such as butane diol, glycols such as dipropylene glycol, glycol monoalkyl ethers, aromatic hydroxy compounds, trimethylol propane, and pentaerythritol. Preferably the initiator should include one or more alkylene oxide groups for the catalyst to function efficiently. Thus, preferably the initiator is first reacted with at least one alkylene oxide to form an oligomer prior to it use to form the polyethercarbonate polyol. Examples include glycerine having from 1 to 6 propylene oxides attached to it, propylene glycol having 1 to 6 propylene oxides, trimethyl propane with 1 to 6 propylene oxides, dipropylene glycol with one or more alkylene oxides attached, sucrose with one or more alkylene oxides attached, sorbitol with one or more alkylene oxides attached, and blends of these oligomers. As would be understood by one of ordinary skill in the art, the oligomer can be reacted with either the same alkylene oxide used during its formation or with another alkylene oxide in the polyethercarbonate polyol formation reaction. The present invention also relates to the preparation of polyurethane forming compositions based on the herein described polyethercarbonate polyols and to polyurethane compounds obtained from said polyurethane forming compositions.To obtain polyurethane compounds, polyethercarbonate polyols may be reacted with compounds which are used in conventional polyurethane forming compositions for the preparation of polyurethanes, such as isocyanates, catalysts, blowing agents, stabilizers, etc.
The isocyanates that may be used include isomers and derivatives of toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). The reaction between the hydroxyl and the isocyanate groups may be catalyzed by tertiary amine catalysts and/or organic tin compounds such as stannous octoate and dibutyltin dilaureate. To obtain a foamed polyurethane, blowing agents may be employed. In addition, stabilizers and flame retardants may be added.